The Time Taken to do the Associativity of App Proof

The time it took us to explain this proof may leave the impression that
the proof is complicated. In a way, it is. But it happens quickly.

The time taken to do this proof is about 1/10 second. The rest of
the time (about 2/10 seconds) is spent in pre- and post-processing.

Basically, this proof flashes across your screen before you can read
it; you see the Q.E.D. and don't bother to scroll back to
read it. You have more important things to do than read successful
proofs.